In video communications applications it is often necessary to transmit at a fixed bit rate. Extra amounts of information transmitted beyond the fixed bit rate may be lost, and transmitting at a lower bit rate would be a waste of bandwidth. When the bandwidth is wasted, video quality is less than ideal. Similarly, when preparing a video stream for media storage, (e.g. DVD) it is desirable to populate the disk to the maximum capacity such that no disk partition is wasted.
Encoded video takes advantage of spatial and temporal redundancies to achieve compression. Even though video encoders make use of sophisticated algorithms to de-correlate spatial, temporal, and spectral sample dependencies, there are still some hidden statistical redundancies which remain embedded in the stream. Thorough identification of such redundancies is advantageous for reducing the size of the final output video stream. Video compression systems can exploit the statistical redundancies in video sources by entropy encoding. Since video sources are non-stationary in statistical sense, advanced entropy coders can take advantage of context modeling to adapt to changes in the source and achieve better compaction. With advanced entropy encoding, bits output from a video encoder can be delayed by the inherent complexity of this encoding technique.
These and other advantages and novel features of the present invention, as well as illustrated embodiments thereof, will be more fully understood from the following description and drawings.